IT’S 8.30am on a Friday, and I’m in an unsalubrious-looking side road just off the A390 next to the Truro branch of Lidl. This route can be nose-to-tail with school and commuter traffic at this time of day; it’s much calmer today, a sure sign both groups are winding down in the run-up to Christmas.

That’s why Devon and Cornwall Police are out in force across Cornwall for Operation Limit, a seasonal push to remind drivers of the dangers of drink and drug-driving. Uniformed traffic officers will wave people into the static site for breathalyser tests and vehicle/document checks. While some will be chosen at random, Moving Traffic Offences – poor driving style, a light out, a misted windscreen - will increase your chances of being pulled in.

The early-morning swoop is designed to warn potential party-goers that alcohol remains in the system much longer than they might imagine. “The body starts processing alcohol half an hour after your last drink, at a rate of one unit per hour,” says PC Dave Langley, road casualty reduction officer for Cornwall. “That means it takes five pints 15 hours to clear your system – and we do not advise people to drive with any alcohol in their system.”

The implication is that a big night out can leave you over the limit the next morning, and while coffee and a shower might make you feel better, they won’t make you road-legal. Get caught, and the consequences range from losing your licence to a maximum penalty of six months in prison, a driving ban of at least one year, trouble travelling to countries like the USA, and an endorsement on your driving licence for 11 years – meaning prospective employers will see your conviction on your licence.

The worst case scenario, of course, is that you hurt or kill yourself - or someone else. Dave recalls a single-vehicle incident when a morning-after driver ploughed his car into a tree. “He survived, but shattered his pelvis.” The man was a builder; on top of the legal implications of the accident, the accident would have had a serious impact on his ability to work.

While the “Don’t drink and drive” message has been hammered home for decades, people still do it. Drink-driving remains one of the ‘Fatal Five’ main causes of injury and death on the region’s roads (the others are excess or inappropriate speed, not wearing a seatbelt, driving while using a mobile phone and careless or inconsiderate driving). Drug-driving is also on the increase, especially in the 18 to 25 age group. Anyone suspected of that today will be asked to carry out a saliva drug swipe.

Christmas sees an uplift in stats, as does summer, when the nights are longer and the beer garden or barbecue beckons. As well as proactive pull-ins, the force sends officers out in marked and unmarked vehicles to spot potential offenders, and also utilises social media and good old-fashioned stickers in strategic locations to encourage people to find a “lift legend”.

Back to this morning, and before the exercise has even started, a young man pulls into the side road of his own free will – through the exit lane, and with a light out. It’s bad luck that he finds himself faced with several marked police cars; three officers wander over for a “chat”. By the time they have finished, his breathalyser is clear but his ears are ringing with advice.

PC Richie Wilson takes up position on the main road, ready to divert drivers in. Truro is his beat, making this job particularly meaningful. “It’s important to me that people are safe on the roads, because I’ve seen the consequences of the opposite, both professionally and personally,” he says. “It’s all too easy to get carried away at Christmas, without thinking about the consequences of driving the next day. As police officers, we are the ones who have to deliver the terrible news to loved ones, so anything we can do to prevent lives being shattered at Christmas is worthwhile.”

Cars start streaming in and out. The vibe is overwhelmingly positive, with the vast majority of drivers chatting and smiling with officers. One tells me: “I’ve no issue at all with it. It’s a good idea at this time of year – and both officers were very kind.”

Occasionally someone will express concern at having to make an appointment or social engagement; PC Scott Barrott gently reminds a woman rushing for a padel match that one should always leave plenty of time to reach one’s destination. “If not, you’re more focused on arriving on time than you are on the road.”

PC Scott is one of three officers from Bodmin with experience on the No Excuses team, a dedicated outfit of 16 that targeted repeat offenders. With the help of Automatic Number Plate Recognition (ANPR) and tip-offs, it was able to make more than 600 arrests and remove dangerous drivers from the roads. He realises this morning won’t see the same impact, but concedes: “In our job, we would pull in five to 10 cars – this will be far more. It’s about getting the message out there, and we can take someone off the road if there is reason to do so.”

By the end of the morning, there have been 41 negative breath tests, one vehicle seized due to the driver not possessing a valid licence and, just as the officers were about to call it a day, an arrest for driving under the influence of drugs – in this case, cannabis. For PC Dave, the perfect morning would see clean results all round, so this isn’t bad.

As I leave, PC Richie is showing a family round his vehicle, letting a little boy sit behind the wheel before posing for selfies. It’s all good PR for the force, while reminding those of driving age: either go easy on the booze at a festive do, or book a designated driver not only for the night itself, but also for the next day.